This invention relates to disposable plastic packaging materials, such as films, wrappers, cups, bottles, trays, cartons and the like used for packaging perishable commodities such as food, condiments, beverages etc, and household products in general. The invention also relates to plastic compositions suitable for use in such packaging materials. More specifically, it relates to plastic packaging materials, and plastic compositions for use therein, which when discarded in an outdoor environment will degrade to become part of the soil, or be washed away by rainfall or wind erosion in a harmless form.
The increasing use of plastic packaging materials which are then discarded has created serious problems of pollution and litter. Because most conventional plastic materials used in packaging have long lifetimes in exterior environments the accumulation of litter of these materials in parks and recreational areas, and even in conventional garbage dumps, has led to many environmental and esthetic problems.
Materials which gradually decompose would, of course solve the litter and pollution problem, provided they decomposed relatively rapidly. Such materials could perhaps be made by including in a packaging plastic an agent which causes the material to decompose. However, against this factor of desirable decomposition must be weighed the requirement that the shelf life of the packaging plastic must be rigidly controlled, and in most cases must be indefinitely long, for proper protection of the perishable contents.
The present invention provides polymeric packaging materials which degrade under the action of the ultraviolet light of the sun, but do not degrade to any appreciable extent otherwise. Thus these polymeric packaging materials start to degrade after they have been discarded in any outdoor environment, but have indefinite storage life indoors, out of contact with direct sunshine.
The wavelengths of light emitted by the sun range from about 2,900A in the ultraviolet to about 20,000A in the infra-red. Only the light with wavelengths ranging from about 4,000 to 8,000A is visible to the human eye. Indoor lighting fixtures emit primarily in this visible range. The present invention is based upon the discovery that there can be introduced into a polymer certain photochemically active chemical groups which do not absorb light of wavelength in the visible range, but do absorb ultraviolet radiation in the wavelength range from 3,000A to 3,500. Having absorbed radiation, the groups cause scission of the polymer chains, and hence degradation of the polymer. Thus the degradation process is not initiated until the polymer is exposed to the ultraviolet light of the sun. Furthermore, because ordinary window glass absorbs most of the ultraviolet radiation of the sun, these polymers will not degrade in sunlight which has passed through window glass. Packages or containers made of these materials could be exhibited in store windows, for example, without initiating the degradation process.
One of the more important classes of plastic materials used for container and packaging purposes are the polyamides such as 6--6 nylon (polyhexamethylene adipamide), 6-12 nylon, polyesters such as polyethylene terephthalate and other polymers coming under the general category of condensation polymers. These polymers break down slowly by photo-oxidation and hydrolysis in an outdoor environment, but molded and extruded objects still retain their shape and an appreciable portion of their original strength for several years under normal weather conditions.